This invention relates to a method for producing superconducting materials of oxide type ceramics and, more particularly, to a method for producing superconducting materials which is improved so that raw materials can readily be uniformly mixed, localization of composition can be prevented and thus uniform compositions can be obtained.
Known superconducting materials include metals (Pb, Hg, La, Ta, Sn, Ti, Zn, In, Nb, Al, V, Tc and the like), alloys (Nb-Tc, Nb-Zr and the like), compounds (Nb.sub.3 Sn, V.sub.3 Si, V.sub.3 Ga, Nb.sub.3 Ge.sub.0.3 Al.sub.0.7, Nb.sub.3 Sn, CeCu.sub.2 Si.sub.2, Mo.sub.6 Se.sub.8, PbMo.sub.6.4 S.sub.8, SnMo.sub.6 S.sub.8, SrTiO.sub.3, BaPb.sub.0.9, Bi.sub.0.1 O.sub.3, LiTi.sub.2 O.sub.4 and the like) and organic materials (TMTSF, BEDT-TTF and the like). Important characteristics of superconducting materials are (1) zero electrical resistance, (2) perfect diamagnetism (Meissner effect) and (3) the Josephson effect. When these materials are utilized for power transmission, power distribution and power generation as a result of the characteristic that their electrical resistance is 0, one of the advantages obtained is that a large current can be obtained with only a small loss thereof. Recently, among the above superconducting materials, oxide type ceramics have been explored in detail because they have a high critical temperature.
The ceramic superconducting materials are generally synthesized by application of powder metallurgy. That is, for example, Y-Ba-Cu-O ceramics (YBCO) are obtained by mixing powders of raw materials BaCO.sub.3, Y.sub.2 O.sub.3 and CuO, calcining the mixture at 900.degree. C. to carry out a solid phase reaction, then grinding the mixture and press molding the resulting powder into pellets and then sintering the molded product in an oxygen atmosphere. In this case, uniformly mixing the above three raw material powders is relatively difficult and besides, mixing requires a long time due to the difference in specific gravity, shape and particle size. Furthermore, there is a problem that the raw materials which constitute the superconducting materials or BaO and CuO in the course of the reaction become liquid phase, which remains as a non-superconducting phase mainly composed of CuO even after cooling, resulting in a reduction of current density. A further problem is that the sintered density decreases owing to the local presence of CuO.